Bacteria are generally found as biofilms in the environment. A biofilm consists of microcolonies of bacteria that are attached to a surface and surrounded by an exopolysaccharide matrix. Biofilm bacteria are more resistant to antimicrobial agents than free-living bacteria and may represent a reservoir of pathogenic organisms in the environment. In the environment, biofilms consist mostly of multiple species. We hypothesize that the presence of different species in a biofilm leads to communication (signaling) between the different species and to changes in gene expression. We will study a biofilm composed of the marine organisms Vibrio cholerae, the causative agent of cholera, and Vibrio harveyi. We propose to analyze the role of known signaling mutants on biofilm formation and to identify signals responsible for the dissociation of bacteria from a biofilm.